M 1

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Polymer Synthesis
CHEM 421
• Odian Book
Chapter 6-2
Copolymers
Polymer Synthesis
CHEM 421
• Copolymers involve the use of two or more monomers
• Copolymers allow us to tailor product properties
– Tg
– Tm
• Commercially important (chain growth) examples include:
– Styrenics
» Styrene/acrylonitrile (SAN): increased impact resistance and solvent
resistance; 10-40% AN, Samsonite luggage
» Styrene/butadiene (SBR): 25% styrene/75% butadiene
» Largest volume synthetic rubber (tires)
» HIPS: High Impact PS (PBD-g-PS)
» Styrene Maleic Anhydride (SMA)
Copolymers
Polymer Synthesis
CHEM 421
• Commercially important copolymers (Cont’d)
–Vinyl chloride
» Rigid PVC: ca. 5% vinyl acetate, lowers Tg small
amount allow to be processed a lower temperatures
avoiding degradation
» Flexible: 20-40% vinyl acetate (tubing, sheets (e.g.
shower curtains, etc.)
» Packaging: Saran Wrap® (90% vinylidene chloride)
Copolymers
• Commercially important copolymers (Cont’d)
– Ethylene (> 10 billion lbs/yr)
» LDPE (homopolymer!)
» High pressure free radical
» 30-40% x-tallinity
» HDPE (homopolymer!)
» Ziegler-Natta
» 75% x-tallinity
» Linear Low Density Polyethylene
» Linear copolymer with 1-5 mol% α-olefins
» EVA: Ethylene vinyl acetate: 2-40% vinyl acetate
» Packaging, molding
» EPR: Ethylene-propylene rubber (plus cure site monomer)
» Ethylene/acrylic acid: (1-10 mol% AA); ionomer
» Surlyn®
Polymer Synthesis
CHEM 421
Copolymers
Polymer Synthesis
CHEM 421
• Commercially important copolymers (Cont’d)
–Fluoropolymers
» PTFE: Tm = 335 °C, Tg = -70 °C
» PVDF: Tm = 180 °C
» FEP: Tm = 250 - 280 °C, Tg = 70 - 120 °C
» ETFE: Tm = 225 °C, Tg = 145 °C
» PFA: Tm = 300 °C
» Teflon AF:
» Nafion:
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
Homo-propagation
Cross-propagation
Terminal Model
Copolymerization Kinetics
…..
Penultimate Model
Polymer Synthesis
CHEM 421
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
Homo-propagation
Cross-propagation
Cross-propagation
Homo-propagation
Terminal Model
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
Rp11 = k11 [M1•] [M1]
Rp12 = k12 [M1•] [M2]
Rp21 = k21 [M2•] [M1]
Rp22 = k22 [M2•] [M2]
Terminal Model
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
The rate of disappearance of M1 and M2 can be expressed as:
d [M1]
- ——— = k11 [M1•] [M1] + k21 [M2•] [M1]
dt
d [M2]
- ——— = k12 [M1•] [M2] + k22 [M2•] [M2]
dt
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
The ratio of the two rates is then:
d [M1]
——— =
d [M2]
k11 [M1•] [M1] + k21 [M2•] [M1]
——————————
k12 [M1•] [M2] + k22 [M2•] [M2]
Simplify:
d [M1]
——— =
d [M2]
[M1]
———
[M2]
k11 [M1•] + k21 [M2•]
——————————
k12 [M1•] + k22 [M2•]
Copolymerization Kinetics
Polymer Synthesis
CHEM 421
Assume the Steady State Approximation:
The concentrations of M1• and M2• are constant
Therefore:
The rate of addition of M1• to M2 will equal
The rate of addition of M2• to M1
k12 [M1•] [M2] = k21 [M2•] [M1]
Define:
r1 =
k11
———
k12
k22
r2 = ———
k21
Copolymerization Kinetics
Copolymer Composition Equation:
d [M1]
——— =
d [M2]
[M1]
———
[M2]
Molar ratio of
the monomers in
the
copolymer
r1 [M1] + [M2]
———————
[M1] + r2 [M2]
Concentrations of
the monomers in the
feed
Polymer Synthesis
CHEM 421
Copolymerization Kinetics
Copolymer Composition Equation:
[M1]
f1 = 1 – f2 = —————
[M1] + [M2]
d[M1]
F1 = 1 – F2 = ———————
d[M1] + d[M2]
F1 =
r 1 f12 + f1 f2
——————————
r 1 f12 + 2 f1 f2 + r 2 f22
Polymer Synthesis
CHEM 421
Copolymerization Examples
Polymer Synthesis
CHEM 421
• r1 = r2 = 1.0
–Monomers exhibit no preference for
homo-propagation vs cross-propagation
–Truly random
copolymer results
1.0
0.8
–F1 = f1
–Ethylene /
vinyl acetate
F1
0.6
0.4
0.2
A
0.0
0.0
0.2
0.4
0.6
f1
0.8
1.0
Copolymerization Examples
Polymer Synthesis
CHEM 421
• r1 = r2 = 1.0
• r1 = r2 = 0.0
–Monomers exhibit tendency to
cross-propagate
1.0
–Alternating
copolymer results
–F1 = 0.5
–Styrene / maleic
anhydride
–TFE / ethylene
0.8
F1
0.6
B
0.4
0.2
A
0.0
–1-Butene / sulfur dioxide
0.0
0.2
0.4
0.6
f1
0.8
1.0
Copolymerization Examples
Polymer Synthesis
CHEM 421
• r1 = r2 = 1.0
• r1 = r2 = 0.0
• r1 and r2 between 0 and 1.0
1.0
–Common
–Cross-over point
» Azeotropic
polymerization
0.8
F1
0.6
B
C
0.4
0.2
A
0.0
0.0
0.2
0.4
0.6
f1
0.8
1.0
Copolymerization Examples
Polymer Synthesis
CHEM 421
• r1 = r2 = 1.0
• r1 = r2 = 0.0
• r1 and r2 between 0 and 1.0
• r1 >> 1.0 and r2 << 1.0
–Significant drift in
feed ratio
1.0
D
0.8
F1
0.6
B
C
0.4
0.2
A
0.0
0.0
0.2
0.4
0.6
f1
0.8
1.0
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